The present invention relates to a fixed gear internal gear hub particularly, although not exclusively, for driving a pedal bicycle wheel.
A fixed gear bicycle (also known as a fixed wheel bicycle) is a pedal bicycle that has no free-wheel. The bicycle pedals are directly connected to the driving wheel of the bicycle and rotate whenever the driving wheel rotates. If the pedals are moved forwards the driving wheel of the bicycle will move forwards and if the pedals are moved backwards the driving wheel of the bicycle will move backwards.
Fixed gear bicycles are currently increasingly popular. Riding a fixed gear bicycle offers a different, and potentially more enjoyable, experience than riding a bicycle with a free-wheel. With a fixed gear bicycle riders may apply force to the pedals to slow and stop the bicycle.
Most fixed gear bicycles are single speed with the bicycle pedals driving a chain connected to a single sprocket fixed to the driving wheel of the bicycle.
To provide for greater flexibility in use, it is desirable to provide pedal bicycles with a transmission enabling the gear ratio between pedals and driving wheel to be changed.
It is known to provide a variable ratio transmission for a pedal bicycle by providing multiple sprockets and means for moving the bicycle chain between the sprockets, the derailleur gear system. However, this system only enables the chain to be moved between sprockets when rotating in one direction, so it is not suited to a fixed gear system.
Variable ratio transmissions are also provided on pedal bicycles by internally geared hub incorporating epicyclic gears. Some such systems, however, incorporate one or more one-way clutches or free-wheels to avoid conflicts between transmission paths. Such arrangements are therefore not suitable for application to fixed gear arrangements.
It is an object of embodiments of the present invention to provide a fixed gear internal gear hub capable of providing two or more transmission ratios, and in particular which improves over existing bicycle transmission arrangements.
According to the present invention there is provided a fixed gear internal gear hub comprising: a fixed axle, an input member and an output member, each rotatably mounted about the axle, an epicyclic gear system comprising at least one sun gear rotatably mounted about the axle, planet pinions disposed in a planet cage and a gear ring, the gear ring being connected non-rotatably to the input member and the planet cage being connected non-rotatably to the output member, a clutch for selectively non-rotatably connecting the input member to the planet cage and a selector key for selectively locking the sun gear rotatably relative to the axle.
Such an arrangement provides for two fixed gear ratios. With the clutch engaged and the selector key disengaged, so that the sun gear may rotate relative to the axle, a direct drive is obtained. With the selector key engaged, preventing the sun gear rotating relative to the axle, and the clutch disengaged a reduction gear is obtained between the input and output members.
The gear ring may be connected to the input member via the clutch. Alternatively the clutch may be connected to the input member via the gear ring.
The output member may be a hub shell rotatably mounted on the axle. The input member may be rotatably mounted between the hub shell and the axle. The hub shell may be mounted to the axle via a ball cup at one end and a ball ring at the opposite end.
The clutch may be axially moveable along the axle relative to the input member. The clutch may be connected to the input member by splines. The selector key may be axially moveable along the axle relative to the sun gear. The clutch and selector key may move together axially. The axle may include a slot and the selector key may be slidably mounted within the slot. A connecting rod may be connected to the selector key. The sun gear may include formations, such as splines, for engaging with the selector key to enable the selector key to lock the sub gear relative to the axle.
Two (or more) sun gears may be provided, together with appropriate compound planet pinions having areas of different diameter with differing numbers of geared teeth for meshing with the individual sun gears. With this arrangement, by selectively locking one of the sun gears a number of different reduction ratios may be provided.
The planet cage may include formations for engaging with the clutch, which may be a dog clutch. The input member may be connected to the gear ring by splines.